This invention relates to a novel organosilicon polymer composed mainly of a carbosilane skeleton and a polysilane skeleton, and to a process for production thereof.
Polymers having a skeleton composed of alternately bonded silicon and carbon atoms with a side-chain organic group bonded to a silicon atom are called polycarbosilanes. Since these polymers are converted to inorganic materials containing silicon carbide as a main component when fired in a non-oxidizing atmosphere, they are suitable as a material for silicon carbide, and are utilized in the form of silicon carbide fibers, sintering aids, impregnating agents, fine silicon carbide powders, etc.
Polycarbosilanes known heretofore include, for example, that disclosed in Fritz: Angew. Chem., 79, page 657 (1967) which is synthesized by thermally decomposing and condensing a monosilane at a temperature of as high as 600.degree. to 800.degree. C. in a flow-type reactor, and that disclosed in U.S. Pat. No. 4,052,430 to Yajima et al. A polycarbosilane partly containing a siloxane bond can be synthesized by the method described in U.S. Pat. No. 4,220,600 to Yajima et al. which comprises adding polyborosiloxane having a phenyl group at least partly in a side chain of Si as a reaction promoter to an organopolysilane, and thermally decomposing and condensing it at 250.degree. C. to 500.degree. C. under atmospheric pressure. These synthesizing methods, however, are industrially disadvantageous because they require high temperatures and a flow-type device adapted for recycling, or require high pressures in a pressurized vessel. Furthermore, when a special reaction promoter such as polyborosiloxane is used, the resulting polymer contains a siloxane bond and therefore, is not suitable when it is desired to minimize oxygen in the fired product
Since these conventional polycarbosilanes can be converted to silicon carbide by firing in an atmosphere of a non-oxidizing atmosphere, they are very useful as a material for thermally stable inorganic materials. Furthermore, because they are soluble in ordinary organic solvents and thermoplastic, they can be converted to molded articles of various configurations. In order to fire these molded articles in their as-molded configurations, they have to be made infusible by curing before submitting them to firing. The most suitable method for curing is to heat the molded articles in the air. For this purpose, it is necessary to heat them gradually to a point near the softening point of the polycarbosilane, or to heat them for a very long period of time at low temperatures. The conventional polycarbosilanes have the defect that the molded articles become molten during heat-curing or curing is not fully achieved and does not extend to the inside of the molded articles It has been extremely difficult to remove these defects.
The present inventors have made extensive investigations in order to remove the above defects These investigations have led to the discovery of a process for producing a novel organosilicon polymer composed mainly of a carbosilane skeleton and a polysilane skeleton, which does not require use of a special device such as a flowtype device adapted for recycling or a pressurized vessel or a special reaction promoter such as polyborosiloxane. The present inventors have also found that the organosilicon polymer obtained by the above process which consists mainly of a carbosilane skeleton and a polysilane skeleton can be more readily rendered insoluble than polycarbosilanes obtained by conventional processes, and have a high residual ratio on firing in a non-oxidizable atmosphere.